C1 Revision

Fractional Distillation

Requires a fractionating column which decreases in temperature with height.

The substance is vapourised.

It enters the fractionating column at the bottom.

The substance is a mixture of different compounds, each with a different condensing point.

This means that as the vapour (gas) rises, the compounds condense at different points meaning they can be pumped away and obtained individually.

The most useful compounds are found at the top of the fractionating column, since they have shorter chains therefore lower boiling points meaning they are good fuels, e.g. petrol. The long chain molecules at the bottom are less useful since they have very high boiling points and are very viscous.

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Formation of Gases on Earth

It is believed that the Earth's surface was completley covered by volcanoes. When they erupted they released carbon dioxide and water.

The gases present in the early atomosphere were:

Carbon dioxide

Water vapour

Other gases

Little or no oxygen.

Whereas now:

78% Nitrogen

21% Oxygen

1% Other gases, including carbon dioxide.

The volume of carbon dioxide decreased due to plants absorbing the carbon dioxide during photosynthesis and the gas dissolving into seas and lakes.

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Metal from the ore

There are three methods of extraction:

1. Carbon reduction and oxidation. A metal oxide reacts with carbon to produce metal and carbon dioxide. This is because the metal oxide is reduced and the carbon is oxidised. This only works however if the metal is less reactive than carbon.

2. Phytomining. The plants are grown on metal compound rich soil. The plants absorb the metal compounds in their roots. The plant is burnt and the ash contains the metal compound which can be extracted.

3. Bioleaching. Bacteria abosorb the metal compounds. They produce a substance called leachate. This contains the metal compound which can now be easily obtained.

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Cracking

It is the process of splitting a long chain hydrocarbon into short chain hydrocarbons. Generally it is used with alkanes.

The long chain alkane splits into a short chain alkane and an alkene.

The process requires a high temperature and a catalyst.

This process is important because short chain, useful hydrocarbons are in short supply but high demand whereas long chain hydrocarbons are in high supply but low demand. This enables us to split up the less useful hydrocarbons into more useful ones to meet the demand.

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Limestone Cycle

Limestone is also known as calcium carbonate, CaCO3.

When limestone thermally decomposes it produces calcium oxide and carbon dioxide. Calcium oxide is also known as quicklime and can be used to remove acidic gases from the chimney of a power station.

When water is added to calcium oxide, slacked lime, calcium hydroxide is produced. It can be used to neutralise acidic soils

If more water is added limewater is produced. We can use limewater to check for the presence of carbon dioxide by bubbling the gas through the liquid, if it is present, the limewater will go cloudy. It goes cloudy due to the production of a solid precipitate called calcium carbonate. The cycle has been completed.

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Polymerisation

It is the joining together of many monomers. Alkenes make good monomers.

An example is the production of polythene from ethene.

The reaction requires heat, pressure and a catalyst.

The double bond in the ethene molecules open up allowing them to attach to each other. This forms a long chain called a polymer. Poly stands for many.

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Hydrogenation

Also known as hardening. It is the process of making an unsaturated liquid fat into a solid saturated fat.

The unsaturated fat is warmed to 60C and hydrogen gas is bubbled through it. The double bond in the unsaturated fat opens up and the hydrogen atoms join to it, forming a saturated fat. It is used to produce substances such as margarine.

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Obtaining vegetable oils

The seeds are sieved to remove stones, etc.

They are then pressed, releasing oil and water.

The water is then drained away, leaving behind the vegetable oil.

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Emulsifiers

They are used to join two immiscible liquids, eg. water and oil.

The emulsifier has two parts, the hydrophilic head and the hydrophobic tail.

The hydrophilic head dissolves into the water droplets, and the hydrophobic tail dissolves into the oil droplets, this prevents the two liquids from regrouping and forming two layers. This creates a stable emulsion which has a better texture and appearence.

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Producing Ethanol

Two methods:

1. Fermentation. Requires glucose from plants. This is fermented in the presence of the yeast catalyst to produce ethanol and carbon dioxide.

It is renewable, requires a lower temperature. However it produces impure ethanol, takes nine months to produce and is produced via batch production.

2. Hydration of ethene. Ethene reacts with steam at a temperature of around 300C. It produces pure ethanol. However it is non-renewable since ethene is produced from crude oil and it requires a lot of energy due to the high temperatures. Although it is a continuous process.

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Cement, Concrete and Mortar

Cemenet - Heat powdered limestone with clay.

Mortar - Cement, sand and water.

Concrete - Cement, sand, water and aggregate.

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Carbonates and Acids

All acids react with carbonates to produce carbon dioxide, a salt and water.